This invention relates to a new and improved small size, breakaway cannula and the process for its manufacture. More specifically this invention provides a breakaway cannula of improved structure for its size that can be mounted inexpensively in low cost, breakaway wings.
Typical publications disclosing breakaway cannula and their manufacture are found in U.S. Pat. No. 3,359,976 to Raymond M. Smith; Swiss Pat. No. 528,271 to Heinz Fuchs and Arthur Eschbach (Nov. 15, 1972); and, U.S. Pat. No. 4,100,393 to Ronald B. Luther.
In the Smith patent, a stamping operation is used to provide the cannula and wing pattern followed by rolling the pattern to the desired cannula shape with integral wings. In the Swiss patent, plastic wings are attached to the proximal end of the cannula by means of an injection molding machine to reduce operating costs and to facilitate splitting the cannula from the proximal end when in use. The Luther patent describes a laser welding operation to attach metal wings to the cannula.
The above types of manufacturing processes for attaching gripping wings to breakaway cannula are suitable if the cannula size is larger than 14 gauge, i.e. larger than about 0.09 inches. However, when manufacturing cannula shown in the Swiss Patent in small sizes of, say, 14-35 gauge diameter, it becomes more difficult to join the wings to the proximal end of the cannula using injection molding techniques. Similarly, both laser welding and pattern stamping techniques become considerably more difficult and time consuming when working with such small cannula.
Another problem associated with a breakaway cannula needle is that it becomes structurally weaker with decreasing size. This situation is aggravated when weakening breakaway grooves are machined or rolled along the cannula itself or on the pre-cannula flatstock. If the weakening grooves could be made smaller, or if the cannula needle wall thickness could be increased, or both, the cannula would of course be stronger.
Still another problem associated with producing grooved cannula is that the cannula must be oriented relative to their grooves prior to sharpening the needle end. This is because the grooves are designed to coincide with the forward and trailing points of the needle. It would be preferred to form and sharpen the needle portion of the cannula without regard to the specific location of the grooves.
Many physicians desire to aspirate blood through the cannula and into the catheter, but this of course, is not possible if a slit cannula is used. If a continuous cannula (i.e. one having no slit) is used instead, it becomes difficult to split away from the catheter. It would be preferred to employ a cannula that can be easily split open, but has a continuous surface with no slit.